The present research proposal is an integral part of an ongoing effort to discover and characterize the neural bases of associative learning. The approach being used in this effort is discussed, as is the suitability of the classically conditioned rabbit nictitating membrane (NM) as a preparation. The specific aim of the research proposed here is to identify, specifically in the rabbit, the group of motoneurons innervating each of the extraocular muscles using retrograde transport of horseradish peroxidase (HRP). This study will identify the actual location of the motoneurons which are the final common pathway for NM extension and those for NM retraction (the gross structures containing these neurons are known to be the abducens and oculomotor nuclei, respectively). This information is an essential prerequisite for future studies which will trace neural inputs to the final common pathway. One extraocular muscle, or a slip of the levator palpabrae superious (which can cause NM retraction), will be injected in each of three newborn and three adult rabbits. The advantages of the HRP method and the problems associated with peripheral HRP uptake in adult animals are reviewed and a possible solution for the latter proposed. Results will be presented in the form of a three-dimensional map showing the relative positions of cell groups which innervate all the extraocular muscles.